Standardization works of international mobile telecommunication (IMT)-advanced which is a next generation (i.e., post 3rd generation) mobile communication system are carried out in the international telecommunication union radio communication sector (ITU-R). The IMT-advanced aims at support of an Internet protocol (IP)-based multimedia service with a data transfer rate of 1 Gbps in a stationary or slowly moving state or 100 Mbps in a fast moving state.
3rd generation partnership project (3GPP) is a system standard satisfying requirements of the IMT-advanced, and prepares LTE-advanced which is an improved version of long term evolution (LTE) based on orthogonal frequency division multiple access (OFDMA)/single carrier-frequency division multiple access (SC-FDMA) transmission. The LTE-advanced is one of promising candidates for the IMT-advanced. A technology related to a relay station is one of main technologies for the LTE-advanced.
A relay station (RS) is a device for relaying a signal between a base station (BS) and a user equipment (UE), and is used for cell coverage extension and throughput enhancement of a wireless communication system.
Many researches for a method of transmitting a signal between the BS and the RS are currently ongoing in the wireless communication employing the RS. A conventional method of transmitting a signal between the BS and the UE has a problem when a signal is transmitted between the BS and the RS.
In the conventional method of transmitting the signal between the BS and the UE, the UE transmits the signal through one entire subframe in a time domain. One reason of transmitting the signal by the UE through the entire subframe is to set a duration of each channel for transmitting the signal to the maximum extent possible in order to reduce instantaneous maximum power consumed by the UE.
However, there is a case where the RS cannot transmit or receive a signal through one entire subframe in the time domain. In general, the RS relays a signal with respect to a plurality of UEs, which results in frequent occurrence of switching between a reception (Rx) mode and a transmission (Tx) mode. Further, the RS can receive a signal from the BS or can transmit a signal to an RS UE at the same frequency band. Alternatively, the RS can receive a signal from the RS UE or can transmit a signal to the BS at the same frequency band. The switching between the Rx mode and the Tx mode requires a specific time (hereinafter referred to as a guard time) between an Rx-mode period and a Tx-mode period. During the guard time, the RS does not transmit or receive a signal in order to avoid inter-signal interference and to provide reliable operations.
In addition, there is a subframe in which the RS must transmit an essential signal such as a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a paging message, to the RS UE connected to the RS. It is difficult for the RS to receive a signal from the BS in such a subframe. For example, in frequency division duplex (FDD), since the RS must transmit the essential signal to the RS UE in subframes having subframe indices 0, 4, 5, and 9, it is difficult to receive the signal from the BS.
Due to the aforementioned restriction, it is difficult for the RS to directly use the conventional HARQ method between the BS and the UE. The HARQ is a technique which combines automatic repeat request (ARQ) with channel coding of a physical layer to increase transmission efficiency in data processing. The ARQ is a scheme in which acknowledgement (ACK) is transmitted to a transmitter when a receiver properly receives data, and not acknowledgement (NACK) is transmitted to the transmitter when the receiver does not properly receive data. When the RS performs an HARQ in a backhaul link, there is a problem in that a subframe in which the RS receives new data or retransmitted data from the BS may overlap with a subframe in which the RS needs to transmit essential information to the RS UE.
Accordingly, in order to solve the aforementioned problems, there is a need for an HARQ method that can be used in a backhaul link between an RS and a BS.